Track circuit for railroads



Aug. 6, 1940 W. H. HOPPE TRACK CIRCUIT FOR RAILROADS Filed Jan. 51, 19:59

INVENTOR oppe Deceased W.H H

W/eyAdminfsTm'trix ATTcir'NE Y Patented Aug. 6, 1940 UNITED STATES 2,210,242 TRACK CIRCUIT FOR RAILROADS Walter H. Hoppe, deceased, late. of Rochester,

N. Y., by Alice Maijgren Hoppe, administratrix, Rochester, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application January 31, 1939, Serial No. 253,836 10 Claims. (Cl. 24634) This invention relates to alternating current track circuit networks and more particularly to a track circuit network in which alternating current of distinctive frequencies is applied to opposite .5 ends of the same track circuit and is an improvement over the invention disclosed in the prior application of Judge, Ser. No. 102,557, filed September 25, 1936, new Patent No. 2,128,211.

In this prior application is disclosed a railway l; signaling system of the single track absolutepermissive-block type, in which only one section of track is employed between successive signals and in which alternating current of distinctive frequencies is applied across the rails at opposite ends of such section. These alternating currents of distinctive frequencies applied to the opposite ends of the track rails between successive signals are necessary to afford a track relay at the entrance end and a source of current at the exit end 9 for trains moving in both directions over the track section to save line wires to facilitate the control of directional stick relays located at the various signal locations and to afford an alternating current source at the exit end of each section for h continuous inductive train control purposes.

In accordance with the present invention, it'is proposed to so organize the track circuit that the alternating current applied to a particular end of a track section will not be impressed, or at least to a slight extent only, across the receiving apparatus located at the end for receiving current from the other frequency source located at the opposite end of the track section. Other objects of the present invention reside in the provision of 3 5 filtering apparatus to freely transmit the current of one frequency and to greatly attenuate and substantially restrict the fiow of current of the other frequency to the receiving apparatus. Another feature of the present invention resides ,gtO 'in'the employment of, in combination with the devices already mentioned, a track relay of the tractive armature type controlled by rectified alternating current derived from the filtering apparatus above referred to.

.45 Other objects, purposes, and characteristic features of the present invention will in part be pointed out hereinafter and will in part be obvious from the accompanying drawing in which Fig. 1

shows a track section of an absolute-permissive- 50 block signalling system to which the track circuit apparatus of the present invention is applied.

Fig. 2 shows graphically the elements and their relation for one track circuit of the track circuit 55 network.

Fig. 3 shows a modified filter which is more sharply tuned to afford a freer flow of current of one frequency and to more greatly attenuate the fiow of current of the other frequency; and

I60 Fig. shows still another modified filter in this winding of the transformer.

which two units such as shown in Fig. 3 are employed in tandem.

Struc ture.Referring to Fig. 1 of the drawing the track rails i and 2 are divided by insulating joints 3 into track sections at the junction of which sections are located signals designated S and S for east-bound trafiic and S and S for west-bound traffic. The devices T, containing suitable exponents, are transformers of the usual construction. The devices I, containing suitable l0 exponents, are inductances. The devices C, con.- taining suitable exponents, are condensers. The devices R, containing suitable exponents, are track relays. The devices IM, containing suitable exponents, are impedances; and the devices RE containing suitable exponents, are rectifiers. The reference character F designates alternating current of a particular frequency, the particular frequency being characterized by the exponent applied to such reference character. 2.0

Referring to Fig. 1 of the drawing, alternating current of frequency F is applied to the transformer T through a condenser C so as to induce an alternating current voltage of this frequency in The secondary g5 Winding of the transformer T is connected across the west endof the track section with an impedance 1M in series with one lead wire of this secondary winding. This impedance 1M is substantially the same in its inductance and resistance. characteristics as that of the track circuit itselfunder average ballast conditions and when there is a train on the track circuit near the end opposite to that where such impedance is located.

Under most favorable conditions, that is, under average ballast conditions and with a train at that .end of the track section remote from the impedance IM there is a zero difference of potential of frequency F between the track rail 2 and the midpoint of the secondary winding of the transformer T This zero difference of potential" results from the fact that one end of the primary winding of transformer T is. connected to the same .point along the potential gradiant of the secondary winding of transformer T as the other end of this primary winding is connected along the potential-loss gradient of the impedance ele- -ments I,.-TR, 2 and 1M in series for frequency F Under this most favorable condition novoltage of frequency F will be induced in the primary winding of the transformer T connected between this midpoint of thesecondary winding of the transformer T and the track rail 2. The imped- 'ance IM has for current of frequency F the same inductive reactance and resistance characteristics as the track rails and the train shunt in series i with average ballast resistance in multiple as does impedance IM for frequency F It is thus seen thatthe current of frequency F under most favorable conditions will not be induced in the primary winding of the transformer T It should also be understood that the impedances 1M and IM in addition perform the usual function'of the usual series impedance of an alternating current track circuit.

This current of frequency F can, however, flow to the east end of track section and through the wheels and axle of the train TR. (see Fig. 2) and when the train vacates the track section can flow through two paths in multiple one of which paths includes the entire secondary winding of the transformer T and also includes the impedance IM and the other multiple path includes onehalf of the secondary winding of the transformer T and includes the primary winding of transformer T The flow of current of frequency F in the primary winding of transformer T causes current of this frequency to be induced in the secondary winding of transformer T and through the medium of the filter; including inductance I condenser C and condenser C causes current of this frequency to be transmitted to the primary winding of the transformer T It may be pointed out that this filter has its inductances and condensers chosen to have values and inductances and capacities, respectively, such that current of frequency F is freely transmitted to the transformer T without substantially any attenuation and such that the multiple path including inductance I and condenser C in series causes substantial attenuation of current of frequency F flowing to this transformer T That is, the units I C in series constitute a shunt for current of frequency F What has been said about the filter including inductance I and condenser C and C at theeast end of the track section is also true of the filter located at the west end of the section and including the inductance I and condenser C and 0*, except that this latter filter is constructed to permit the flow of current of frequency F to the transformer T without any substantial attenuation and so as to greatly attenuate the current of frequency F this attenuation of current of frequency F being primarily accomplished by the shunt path including inductance I and condenser C in series, which permits the free fiow of current of frequency F i The condenser C included in series with the primary winding of transformer T is employed to adjust the impedance characteristic of the transformer T so as to more freely permit the flow of current of frequency F through the lefthalf portion of the secondary winding of this transformer T to the primary winding of the transformer T The condenser C is used for a similar purpose in series with the primary winding of the transformer T insofar as the flow of current of frequency F to the primary winding of the transformer 'I is concerned. The filters, such as the filter including thesecondary winding of the transformer T and the primary winding the track location of the signals S and S in such a diagrammatic manner that it can be readily seen why the transformer T cannot induce any current into the transformer T when the impedances of elements I, 2, and TR are equal to the impedance 1M namely, under the most favorable ballast and track occupancy conditions, the impedances being based on a current of F frequency. The filters shown in Fig. 1 of the drawing effect rather pronounced separation of the currents of frequency F and F but if more pronounced separation is desired, that is, if sharper tuning is desired, a filter such as shown in Fig. 3 employing the additional condenser C may be employed. If still sharper tuning or filtering is desired, two such filtering arrangements, such as shown in Fig. 3, may be connected in tandem as shown in Fig. 4 of the drawing.

Operation.Under normal trafiic conditions, that is, when there are no trains in the track section, the alternating current of frequency F flows with very little attenuation to the receiver including the rectifier RE and the track relay R and at the same time current of frequency F can flow with very little attenuation from'the east end of the track section to the receiver including the rectifier RE and track relay R 10- cated at the west end of the track section, When a train enters the track section it will, of course, short circuit the track rails and will substantially shunt the receiver including relay R from the alternating current source of frequency F and will substantially shunt the receiver including track relay R from the alternating current source of current of frequency F Also, the entrance of this train on the track circuit will establish the proper balance between the track circuit impedance and the impedance 1M and IM for the respective frequencies of current applied at their respective ends of the track circuit, so that in each instance the current source at that end of the track section will not be induced into the transformer feeding the receiver at that end,

namely, the transformer T cannot feed the trans former T for the east end of the track section and the transformer T cannot feed the transformer T for the west end of the track section, The presence of such train, of course, effects the de-energization of both of the track relays R and R and will result in proper controlof the wayside signals and associated apparatus of the absolute-permissive block signaling system through the medium of contacts on these relays, shown conventionally.

Having thus shown and described one specific embodiment of the present invention together with several modified embodiments of filters that may be used as an element of that invention, it is desired tobe understood that the specific circuit network illustrated may be modified Without departing from the spirit or scope of this invention, except as demanded by the scope of the following claims.

What is claimed as new is:

1. In a track circuit network, the combination with a section of track, a source of alternating current of one frequency connected across the track rails at one end of said section, an impedance unit having an impedance value substantially equal to the impedance of the track rails of said track section when shunted by a train near the opposite end of said section for a current of a second frequency, a transformer having its secondary windof said secondary winding and the track rail to which said impedance unit is connected, 9; scurce of current of'said second frequency connected to the primary winding of said transformer, and means at times responsive to current ofsaid second frequency when said track section is unoccupied, whereby current from said source of said first frequency flows freely to said receiver and current from said source of said second frequency cannot freely flow to said receiver when said track section is occupied near said one end. 2. In a track circuit network, the combination with a section of track, a source of alternating current of one frequency connected across the track rails at one end of said section, an impedance unit having an impedance value substantially equal to the impedance of the track rails of said track section when shunted by a train near the opposite end for a current of a second frequency, a'transformer having its secondary winding connected across the other end of said track section with said impedance in series therewith, a receiver tuned to receive current of said one frequency connected between an intermediate point of said secondary winding and the track rail to which said impedance unit is connected, a source of current of said second frequency connected to the primary winding of said transformer, and means connected to the track rails at said one end of said section responsive to current of said second frequency, whereby current from said source of said first frequency flows freely to said receiver and current from said source of said second frequency cannot freely flow to said receiver. I i

3. In a track circuit network, the combination with a section oftrack, a source of alteratine current of one frequency connected across the track rails at one end of said section, an impedance unit having an impedance value substantially equal to the impedance of the track rails of said track section when shunted by a train near the opposite end of said section for a current of a second frequency, a transformer having its secondary winding connected across the'other end'of said track section with said impedance in series therewith, a receivertuned to receive current of saidone frequency and to greatly attenuate current of said second frequency connected between an intermediate point of said secondary winding andthe track rail to which said impedance unit is connected, a source of current of said second frequency connected to the primary winding of said transformer, and electro-responsive means connected to the track rails at said one end responsive to current of said second frequency, whereby current from said source of said first frequency flows freely to said receiver and current from said source of said second frequency cannot flow freely to said receiver but can actuate said electro-responsive means.

4. In a track circuit network, the combination with a track sectionQtwo impedances, two transmitting transformers each having an intermediately tapped secondary winding and having their secondary windings connected across the rails at the opposite ends of said track section one secondary winding in series with one of said'impedances and the other secondary winding in series with the other of said impedances,

two alternating current sources of different frequencies one connected across the primary winding of one of said transformers and the other connected across the primary winding of the other of said transformers, said impedances having values of inductance and resistance substantially equal to the inductance and resistance of the rails of said track section when shunted by substantially block the flow of alternating current of the frequency applied to the adjacent end of said track section, and current responsive means connected to each of said filters.

5. In a trackcircuit network, the combination with a section of trackincluding track rails and ballast leakage paths from rail to rail; two impedances, each having ohmic resistance and inductance of substantially the same value as the track circuit of said track section for average ballast conditions and when occupied by a train near the opposite end; a transmitting transformer at each end of said section, each having a tap brought out from its secondary winding at an intermediate point and having its secondary winding connected in series with one of said impedances across the rails of said track section;

two sources of alternating current of different frequencies; one connected across the primary winding of one of said transmitting transformers and the other connected across the primary winding of said othertransmitting transformer; two filters, one connected from the tap of one trans.- mitting transformer to the rail to which its associated impedance is connected and the other connected from' the tap of the other transmitting transformer to the rail to which its associated impedance is connected; each filter being constructed to pass alternating current of the frequency applied to the opposite end of the track section and to greatly attenuatealternating current of the frequency applied to the track rails at the adjacent end of saidtrack section; and receiving devices connected to saidfilters.

6. In a track circuit network; the combination with a section of track including track rails and ballast leakage paths from rail to rail; two impedances, each having impedance of value-and power factor of substantially the same value as said track section for certain frequencies and for average ballast conditions when there is a train 1 near the opposite endin said section; a transmitting transformer at each end of saidsection,

and the other connected from the tap of theother transmitting transformer to therail to which its associated impedance is connected; each filterbeing constructed topass alternating current of the frequency applied to the opposite end of the track section and to shunt away alternating current of the frequency applied to the track rails at the adjacent end of said track section; and receiving devices connected to said filters.

.7. In a track circuitnetwork; the combination with a section of track including track rails and ballast leakagepaths from railto rail; two impedances, each having ohmic resistance and inductance of substantially the same value as said track section when shunted by a train at the far end for average ballast conditions; a transmittingtransformer at each end of said section, each having a tap brought out from its secondary winding at an intermediate point, said secondary winding being connected in series with one of said impedances across the rails of said track section; two sources of alternating current of different frequencies, one connected across the primary winding of one of said transmitting transformers and the other connected across the primary winding of said other transmitting transformer; two filters, one connected from the tap of one transmitting transformer to the rail to which its associated impedance is connected and the other connected from the tap of the other transmitting transformer to the rail to which its associated impedance is connected; each filter comprising two filter units connected end-amend, each of. said filter units being constructed to pass alternating current of the frequency appliedto the opposite end of the track section and to greatly attenuate alternating current of the frequency applied to the track rails at the adjacent end of said track section; and a relay connected to the out-put end of each of said filters.

8. In a track circuit'network; the combination with a section of track including track rails and ballast leakage'paths from'rail to rail; two impedances, eachhaving ohmic resistance and inductance of substantially the same value as said track section when shunted by a train at the far end for average ballast'conditions; a transmitting transformer'at each end of said section, each having a tap broughtout from its secondary winding'at anintermediate point, the secondary winding of said transformer being connected in series with one-of said impedances across the rails of'said track section; two sources of alternating current of different frequencies, one connected across the primary winding of one of said transmitting transformers and the other connected across the primary winding of said other transmitting transformer; two filters, one connected from the tap of one transmitting transformer to the rail to which its associated impedance is connected and the other connected from the tap of the other transmitting transformer to the rail to which its associated impedance is connected; each filter being constructed to pass alternating current of the frequency applied to the opposite end of the track section and to greatly attenuate alternating current of the frequency applied to the track rails at the adjacent end of said track section; receiving devices connected to said filters; and a condenser in series with the primary winding of each of said transmitting transformers of a capacity to aid the flow in the secondary winding thereof of current of the frequency applied to the opposite end of the track section.

9. In a track circuit network, the combination with'a track section, two impedances, two transmitting transformers each having an intermediately tapped secondary winding and having their secondary windings connected across the rails at the opposite ends of said track section one secondary winding in series with one of said impedances and the other secondary winding in series with the other of said impedances, two alternating current sources of different frequencies one connected across the primary winding of one, of said transformers and the other connected across the primary winding of the other of said transformers, said impedances having an impedance value for the frequency of the alternating current source connected across the primary winding of the transformer in the secondary winding of which they are included substantially equal to the impedance at the same frequency of the rails of said track section when shunted. by a train near the opposite end, two receiving transformers one connected between the tapof one transmitting transformer and the rail end of its associated impedance and the other connected between the tap of the other transmitting transformer and the rail end of its associated impedance, a filter connected to the secondary winding of each of said receiving transformers, each filter being tuned to transmit current of the frequency applied at the opposite end of said track section and to substantially block the-flow of alternating current of the frequency applied to the transformer to which its associated receiving transformer is connected, and current responsive means connected to each of said filters.

.10. In a track circuit network; the combination with a section of track including track rails and ballast leakage paths from rail to rail, two impedances, each having ohmic resistance and inductance of the same value as said track section when shunted by a train at the far end for average ballast conditions; a transmitting transformer at each end of said section, each having an intermediate tap1brought out from its secondary winding, said secondary winding being connected in series with one of said impedances across the rails of said track section; two sources of. alternating current of different frequencies,

one connected across the primary winding of one of said transmitting transformers and the other connected across the primary winding of said other transmitting transformer; two filters, one

connected from the intermediate tap. of one transmitting transformer to the rail to which its associated impedance is connected and the other connected from the intermediate tap of the other transmitting transformer to the rail to which its associated impedance is connected; each filter comprising two filter units connected endto-end, each of said 'filter'units being constructed to pass alternating current of the frequency applied to the opposite end of the. track section and to greatly attenuate alternating current of the frequency applied to the track rails at the ad- J'acent end of said'track section; a relay connected to the out-put end of each of said filters; and railway signalling apparatus controlled by said relays.

q ALICE MAIJGREN'HOPPE, Administratrix of the Estate of Walter H. Hoppe,

Deceased. 

